It means that row 5 will be the public (or right side, RS) of the piece, the side that faces outward. The next rows are going to be stockinette stitch with the knit side as the RS.
Since the pattern is given in rows and not rounds, it sounds like you're just using circulars to knit back and forth (knitting flat) without joining. Maybe the pattern asks for circulars because you have a large number of stitches? What is the pattern that you're making? is there a pattern link?

It becomes important later when you've finished the main part of the afghan and are ready to add the border. The pattern is making sure you understand which side it's calling the right side because that's the side from which you'll be picking up stitches.
It may also help to mark the right side (RS) of the afghan so that you'll be sure to knit the rows on the right side and purl the rows on the wrong side (WS). A safety pin or a loop of yarn will work.
Very nice project. We'd love to see a photo of the finished afghan if you'd like to post one.

It's good to get accustomed to things like making sure you know which is the RS or WS with simpler patterns. As you move on to more complicated things it becomes more important. Working stockinette, the RS will be pretty obvious but you will probably encounter patterns where it's not and if you're at all like me will sit there trying to figure out which side you really are on when you forget to mark it. That's going to be pretty when you're done, what yarn are you using?

__________________~ GG

Cheating is an option. . . . Cheaters never win and winners never cheat, but smart knitters who want to retain an iota of sanity do, cheerfully. ~~Kory Stamper

It's good to get accustomed to things like making sure you know which is the RS or WS with simpler patterns. As you move on to more complicated things it becomes more important. Working stockinette, the RS will be pretty obvious but you will probably encounter patterns where it's not and if you're at all like me will sit there trying to figure out which side you really are on when you forget to mark it. That's going to be pretty when you're done, what yarn are you using?

My son picked some interesting colors so I'm not sure how "pretty" it will be! He chose a shade of green, light blue, and some red. We picked some yarn we found in Hobby Lobby "I Love This Yarn super soft". My son really liked how it felt!! This is only the second project I've attempted so I like how easy it is. And yes, I'm now learning what "right side" means.

It becomes important later when you've finished the main part of the afghan and are ready to add the border. The pattern is making sure you understand which side it's calling the right side because that's the side from which you'll be picking up stitches.
It may also help to mark the right side (RS) of the afghan so that you'll be sure to knit the rows on the right side and purl the rows on the wrong side (WS). A safety pin or a loop of yarn will work.
Very nice project. We'd love to see a photo of the finished afghan if you'd like to post one.

I understand now! I need to know the right side to finish. Got it!!! Thank You!!!

You're off to a good start! Your son will love the colors he chose so what anybody besides you and he think isn't important. Still, I bet it will be lovely! I do hope we get to see it. Happy knitting!

I did a crocheted blanket for my granddaughter in bright pink and bright green. That one I couldn't finish fast enough to be rid of it but she loves it. The customer (recipient in this case) is always right, right?

__________________~ GG

Cheating is an option. . . . Cheaters never win and winners never cheat, but smart knitters who want to retain an iota of sanity do, cheerfully. ~~Kory Stamper